Petrophysical characterization of tight oil formations using 1D and 2D NMR

Porosity and fluid types in pores are crucial parameters in evaluating the quality of a tight oil reservoir in both laboratory analyses and log interpretation. As an advanced technique, nuclear magnetic resonance (NMR) has been applied in oilfields to acquire specific petrophysical properties of rocks. In order to interpret NMR data collected from actual oil wells more accurately, it is necessary to perform experiments in the laboratory and then make a well-designed contribution. Due to the complex components of low-permeable rocks, the petrophysical characterization of tight oil formations with both 1D and 2D NMR techniques remains a challenge. In this study, we designed novel NMR experimental procedures to characterize petrophysical properties of tight oil formations. We first investigated optimal parameters for measuring porosities of core samples. In order to explain the porosity differences between NMR porosity and water porosity, we examined contents of hydrogen-bearing matters and studied their total effects on measured porosity. Then, we performed a series of experiments to make core samples in five states, including water saturated state, after-centrifugation state, light oil saturated state, fresh state, and oven drying state. Each state represented a special fluid type, and hydrogen-bearing matters in cores were tried to be identified. Based on experimental results and similarity analyses, identification graphs of hydrogen-bearing phases were made by using 1D T2 spectrums and a 2D T1-T2 map. Our results can not only expand the applications of NMR core analyses, but also help to interpret NMR logging data better.